J. Warshauer - Accessing non-equilibrium states of correlated materials through targeted ultrafast optical excitation

Strongly correlated materials provide rich platforms through which to explore interesting non-equilibrium states using the pathways provided by the complex interactions of spin, orbit, charge, and lattice degrees of freedom. Ultrafast laser pulses allow us to disentangle the transient dynamics of these non-equilibrium states and potentially open the door to tunable control of material properties or the discovery of novel phases. In this work, we investigate the rich interplay between the lattice and electronic structure of the iron-based superconductor parent compound BaFe2As2, uncovering a transient gap generation driven by coherent lattice vibrations. Exploring the nature of the spin-orbit-entangled exciton series of the van der Waals antiferromagnet NiPS3, we find a long-lived, photo-induced state characterized by a negative THz photoconductivity, which we interpret as a population inversion state. Finally, we apply our photoexcitation scheme in bulk NiPS3 to analyze photocarrier densities, from which we discern the dominant carrier generation mechanisms, identify the onset of interband transitions, and estimate the spin-orbit-entangled exciton binding energy. These results provide key insights into the electronic and excitonic characteristics of NiPS3 and reveal useful non-equilibrium states generated through targeted photoexcitation in correlated materials.